The invention relates to a balloon catheter comprising a catheter tube having mounted thereon at least two balloons adapted to be expanded by internal pressure.
Balloon catheters are introduced into blood vessels so as to eliminate stenoses, i.e. narrowed regions caused by depositions, by way of dilatation. A balloon catheter comprises a high pressure balloon which is in a folded configuration during the insertion of the catheter and, after stenosis has been attained, is inflated by filling it with a liquid. The process of inflation involves the application of a relatively high pressure in the range of about 3-20 bar. The high pressure balloon will thereby spread apart the narrowed region, thus effecting a permanent enlargement of the cross section of the opening at the site.
Further, it is known to arrange a tubular metallic coronary stent around the balloon, with the stent being likewise widened by the expansion of the balloon and remaining in the artery after withdrawal of the catheter. During the implantation of the coronary stent, the balloon may cause fissures in the adjacent vessel wall (peristent dissection). This is due to the fact that the balloon is expanded not only in the stent region but also outside the stent while pressing with a high force against the vessel wall at the transition site. In case of a peristent dissection, the need may arise to implant an additional stent in the vicinity of the originally inserted stent to thus cover the dissection. Alternatively, an attempt can be made to prevent an excessive expansion in the peristent region by avoiding a high balloon pressure and by underdimensioning the stent. This approach, however, entails the danger that the stent is expanded insufficiently. Further, there is a risk of premature closure and restenosis.
A further problem in balloon catheters resides in that the elongate balloon, which is expanded at a high pressure, will stretch the artery into a linear shape along the whole length of the balloon even if the natural course of the artery on this site is curved.
Known from U.S. Pat. No. 4,748,981 is a balloon catheter comprising two balloons arranged within each other. This balloon catheter serves for performing two dilatation processes at different sites of the artery sequentielly andxe2x80x94optionallyxe2x80x94with different diameters, while obviating the need to exchange the catheter.
A balloon catheter provided with two balloons forming the basis of the precharacterizing part of claim 1 is known from DE 195 26 784 A1 and DE 297 04 280 U1. This balloon catheter comprises a first balloon to be used for placing a stent, and a second balloon arranged on the catheter tube at a distance from the first balloon and provided as a dilatation balloon. First, the second balloon is arranged in the region of the stenosis and is expanded. Thereafter, the catheter is advanced so that the first balloon, which carries a stent, will be placed in the stenosis. In the above balloon catheter, the first balloon can be provided as a high pressure balloon and the second balloon can be provided as a low pressure balloon.
It is an object of the invention to provide a balloon catheter designed to avoid dissections of the vessel wall and thus allowing for a harmless vessel dilatation.
According to the invention, the above object is achieved by the features indicated in claim 1.
The balloon catheter according to the invention comprises, in addition to the first balloon, at least one second balloon immediately adjacent thereto. In their expanded condition, the first and second balloons will form a support which in the longitudinal direction is not interrupted by constrictions, i.e. the balloons directly merge into each other; in the expanded condition, both balloons have the same diameter or the first balloon has a slightly larger diameter than the second balloon. In no case, the diameter of the first balloon is smaller than that of the second balloon. Both balloons present an uninterrupted support face extending along the complete length of the balloon region, which can be applied on the vessel wall. While the first balloon is subjected to a high pressure in the range of 15 bar, the second balloon is expanded with a lower pressure in the range of about 6 bar. As a result, a balloon portion adapted to be fully expanded is available along the complete length of the balloon, followed by a contiguous further balloon portion which is expanded to a lesser extent. In the expanded condition, the overall balloon region is of a gradually varying rigidity or stiffness, thus avoiding a sharp transition to the hard balloon portion. To begin with, this offers the advantage that, after insertion of the balloon region, the second balloon can be first expanded for fixing the balloon region in place in the artery. During the subsequent expanding of the first balloon, the latter cannot slide off the stenosis and be accidentally displaced in the longitudinal direction. A further advantage resides in that the second balloon has a certain deformability and flexibility and thus is better suited to attain a shape conformal with the curved course of the artery. As compared with the presently customary balloon catheters, the high pressure balloon can be configured with a shorter length and thus will act in a well-aimed manner only upon the region of the stenosis.
In use, the balloons referred to as high pressure balloons and low pressure balloons are inflated with a higher pressure and a lower pressure, respectively. This, on the other hand, is not to say that these balloons should consist of different materials or have different pressure stress resistances. Basically, both balloon types may be designed for operation by a high pressure up to 25 bar.
Advantageously, the balloon catheter according to the invention can be used also for stent implantation. In this case, the stent is arranged to extend in the longitudinal direction up into the region of the second balloon. Thus, the stent is expanded and pressed against the vessel wall with different forces in different regions. The region at the end of the stent is subjected merely to the relatively small expansion force of the low pressure balloon so that the portion of the low pressure balloon projecting beyond the stent will reduce the danger of peristent dissections The soft outer balloon serves inter alia for the fixing and stabilizing of the stent so that the stent does not slide off the hard inner balloon. By way of alternative, the stent can be placed to extend only along the first balloon while not projecting along the second balloon.
Preferably, the high pressure balloonxe2x80x94when viewed in the longitudinal direction of the catheter tubexe2x80x94is arranged centrally within the second balloon, wherein the sum of the length of the two portions of the second balloon is at least as large as the length of the first balloon. However, it is also possible to arrange a respective second balloon on each side of the first balloon. It is imperative that the first balloon and the second balloon be inflatable separately from each other via different lumina of the catheter tube, with both balloons being inflated in the operative state. Upon expansion of the stent, the low pressure balloon is expanded first. In the process, merely a relatively low trauma is caused to the normal vessel area external of the stent. The low expansion pressures of xe2x89xa66 bar in the second balloon are sufficient for optimum expansion of the stent in the healthy vessel regions and in the peristent regions. Subsequently, the first balloon is expanded with a higher pressure. In this manner, a controlled overexpansion is brought about in the stenosis region within the stent to thus obtain a maximum expansion there.
Due to insufflation of the high pressure balloon, a pressure may be exerted on the low pressure balloon, thus requiring that liquid be discharged from the low pressure balloon. For this purpose, the low pressure balloon is preferably connected to a pressure source which, should the low pressure be exceeded, allows for a backflow of the pressure fluid introduced into the low pressure balloon and thus effects a pressure relief.